The physical and electronic properties of aluminum nitride (AiN) give it great potential for a wide variety of semiconductor applications. AlN has a wide energy bandgap (6.2 electron volts), high breakdown electric field and extremely high thermal conductivity. In fact, in Chow et. al Wide Bandgap Compound Semiconductors for Superior High Voltage Unipolar Power Devices (IEEE Transactions on Electron Devices, Vol. 41, No. 8, 1994) ranking all semiconductors materials, AlN is reported to have, excluding diamond, the highest figure of merit for unipolar power device performance.
In addition, the high thermal conductivity and high optical transmissivity (i.e., low optical density) of AlN make AlN an excellent candidate substrate material. Also, AlN is likely to be the optimum substrate for the growth of pseudo-binary inter metallic compounds such as Al.sub.0.8 In.sub.0.2 N which have extremely high figures of merit for semiconductor performance (up to 4,413,000 times silicon). Although AlN has extraordinary properties for a semiconductor material and has tremendous commercial potential, AlN based semiconductor devices have been limited by the unavailability of large, low defect AlN single crystals. In the most successful prior work, Slack and McNelly demonstrated a method for growing AiN single crystals via sublimation in AlN Single Crystals (Journal of Crystal Growth 42, 1977). However, the time required to grow a 12 mm by 4 mm crystal was approximately 150 hours. This growth rate is far too low to ever allow the commercial production of AlN single crystals.
AlN has been alloyed with silicon carbide (SiC) in monocrystalline thin films produced, for example, by liquid phase epitaxy. Polycrystalline AlN:SiC alloys have also been produced by isostatic pressing processes. However, bulk single crystalline (monocrystalline) alloys of AlN:SiC have not been commercially produced.
Certain monocrystalline AlN:SiC alloys have promise for use as substrate materials that have superior electronic properties to either AlN or SiC. Physical and electronic properties can be tailored to specific device applications by selecting a specific AlN:SiC alloy composition. For example, certain AlN:SiC alloys are direct bandgap materials which is an important property for optoelectronic and other devices. Furthermore, AlN:SiC alloys have other desirable electronic properties such as high electron break down field, high saturated electron drift velocity, high thermal conductivity and a wide energy bandgap. Accordingly, there is a need for apparatus and processes for growing bulk single crystalline alloys of AlN:SiC, particularly such single crystalline alloys that are tailored in their makeup to meet specific needs, for example, specific needs in the electronics industry.